The present invention relates to an expandable honeycomb structure such as used for window coverings. The structure is made of foldable material which in the expanded condition defines a plurality of longitudinally extending cells, one on top of the other. In the retracted state of the honeycomb structure, the adjacent cells are collapsed on each other.
The prior art discloses various honeycomb structures made from foldable material. Representative of such prior art are the Rasmussen U.S. Pat. Nos. Re. 30,254, and Re. 31,129, the Suominen U.S. Pat. Nos. 4,288,485 and 4,388,354, and the Masuda U.S. Pat. No. 3,164,507. In addition, U.S. Pat. No. 4,450,027 to Colson discloses a honeycomb structure constructed from foldable material which is folded longitudinally of the material and wound onto a rack in overlying layers. The layers are adhered together to form the cells of the honeycomb structure. The present invention is most directly a variation of the honeycomb structure and method of making it as disclosed in the '027 patent.
In constructing honeycomb structures from a single length of material in accordance with the teachings of the '027 patent, the opposite longitudinal edges of the length of material are progressively folded over one side of the material. Adhesive is then applied to the exposed longitudinal edges whereby they adhere to the overlying layer of folded material as it is wound onto the rack. With the single folded construction of the '027 patent, the application of the adhesive must be carefully controlled so as not to interfere with the processing operation and in particular, the stacking operation. Also, the choice of adhesive used must be carefully chosen to be compatible with the material from which the honeycomb structure is being formed. Improper choice and application of adhesive can produce an unacceptable product.
Where the honeycomb structure is to be used for window coverings or panels, it is often desirable to fabricate the honeycomb structure from somewhat porous material. This is desirable to give, for example, a translucent effect to the honeycomb structure when, in its expanded condition, covering a window. With porous material, there is an increased tendency for any adhesive to bleed through the material. This in turn, can result in the opposite walls of the individual cells becoming adhered together as they are wound onto the rack in overlapping layers. Examples of suitable materials are non-woven fibers of polyester, woven material from plastic or textile fibers plus plastic. Also, laminates can be used. With these materials, it will be the absorbtion in and through a somewhat porous layer that creates the bleeding through problem. When this results, the product is either unusable or the cells must be carefully pulled to their expanded condition before the adhesive has fully set. This sometimes is not possible or feasible, and, in any event, it increases the manufacturing costs.
In addition to manufacturing problems which can result from improper application of the adhesive, the choice of adhesive can also result in an unsuitable product. Honeycomb structures as used for window openings are, in many situations, subjected to continuous and severe sun conditions. These conditions can have an adverse affect on the adhesive causing separation of the adjacent cells. Obviously, this is undesirable. Although suitable adhesives to prevent this are available, they may be incompatible with the manufacturing process as discussed above.
Another aspect of the honeycomb structures of the prior art relates to the creasing or pleating of the material along fold lines to form each cell. One reason pleating is provided is to assist in the orderly collapsing of the individual cells as the structure is moved between an expanded and a retracted position. Without pleats, the collapsing of the cells would tend to be haphazard and not give a neat appearance to the structure.
In the cell construction disclosed in the '027 patent, the pleats are formed to be permanent so that the faces of the honeycomb structure extend in an angular configuration in the expanded condition of the structure. If the pleats are not carefully and properly formed, they will tend to hang out. This is especially so after long, continued use of the structure with the expanded condition being one where the cells lie one below the other. In such an orientation, the weight of the structure itself pulls on the material of the overlying cells with the greatest forces being exerted at the top of the structure by the entire weight of the underlying cells. Any falling out of the pleats tends to increase the overall height of the structure over the height as initially manufactured. The effect of this can be unpleasing and unsatisfactory, both aesthetically and physically.